Elbow hinge joint anatomy

Steps:

• Identify the elbow as a hinge joint allowing flexion/extension between upper arm and forearm bones.
• Recall primary bones: humerus (upper arm) articulates with ulna (forearm) at the trochlea-trochlear notch.
• Examine diagram labels: 1 as humerus, 4 as ulna, forming the main hinge.
• Exclude radius (likely 2 or 3), which contributes to rotation via pivot joint.

Why B is correct:

• The elbow hinge is defined anatomically as the humeroulnar joint between humerus (1) and ulna (4), enabling uniaxial movement per synovial joint classification.

Why the others are wrong:

• A: Includes 2 (radius), which forms the radioulnar pivot, not the hinge.
• C: Includes 3 (likely radius or accessory), extraneous to the primary hinge articulation.
• D: Omits humerus (1), including only forearm bones (2 and 4), which do not form the elbow hinge.

Final answer: B